“The Las Vegas gunman transferred $100,000 overseas in the days before the attack and planned the massacre so meticulously that he even set up cameras inside the peephole of his high-rise hotel room and on a service cart outside his door, apparently to spot anyone coming for him,” authorities said, AL JAZEERA reported.

Meanwhile, investigators are taking a harder look at the shooter's girlfriend and what she might have known about the attack at a country music festival, with the sheriff naming her a ‘person of interest’.

The girlfriend, Marilou Danley, 62, returned to the United States from the Philippines on Tuesday night and was met at Los Angeles International Airport by FBI agents, according to a law enforcement official.

The official was not authorized to publicly discuss the matter and spoke to The Associated Press news agency on condition of anonymity.

Authorities are trying to determine why Stephen Paddock killed 58 people in the deadliest mass shooting in modern US history.

“They have been speaking with Danley, who was out the country at the time of the shooting, and we anticipate some information from her shortly," Sheriff Joseph Lombardo said hours before she arrived.

Lombardo said that he is ‘absolutely’ confident authorities will find out what set off Paddock, a 64-year-old high-stakes gambler and retired accountant who killed himself before police stormed his 32nd-floor room.

Authorities released police body camera video that showed the chaos of the attack as officers tried to figure out the location of the shooter and shuttle people to safety. Amid sirens and volleys of gunfire, people yelled "they're shooting right at us" while officers shouted "go that way!"

Clark County Undersheriff Kevin McMahill said the shooting spanned between nine and 11 minutes.

Paddock transferred $100,000 to the Philippines in the days before the shooting, a US official briefed by law enforcement but not authorized to speak publicly because of the continuing investigation told The Associated Press news agency.

Investigators are still trying to trace that money and also looking into a least a dozen financial reports over the past several weeks that said Paddock gambled more than $10,000 per day, the official said.